Within shock absorber valve technology, a clear need has arisen to produce a pressure regulator having a bleeder-like character, which means that its opening pressure must as far as possible approach zero when the flow approaches zero. The pressure regulator must additionally have a low “blow off” or “cracking pressure” opening point, here referred to as the opening pressure, for all settings, modulations or spring biases, despite the fact that at higher pressures it must generate high pressures within the working range.
A known embodiment of a pressure regulator having a bleeder-like character comprises a spring arrangement consisting of a first spring and a second spring, in which the first spring biases the second spring and contributes to different spring characters in different parts of the stroke. A low spring constant is used initially at the start of the stroke and the low spring constant then transforms into a higher spring constant which is suited to high pressures and dynamic sequences in connection with rapid damping motions. The broken character here produces a low spring constant close to the closed position with a view to giving an accurate setting of the bias. In order to stabilize the valve behavior and avoid noise problems caused by friction forces when the valve changes from closed to open position and vice versa, the accurately set valve must be given an extremely low bias. Such extreme accuracy per se leads to a more expensive production process, but still has lower costs compared with the accuracy which is demanded in the process if low bias is to be achieved with just a stiff spring.
Due to this noise problem and difficulties with the accuracy for the length tolerances of springs, pressure regulators including only one spring, for example shock absorber check valves, must instead be given a high bias in the closed position, which sometimes leads to difficulties in attaining the desired low damping levels for low speeds and small valve flows.
The above-described problems apply to all biased cone valves, pilot valves, pilot-controlled valves and direct-controlled valves, including check valves. The common denominator of these valves is that the pressure which is regulated acts in an opening direction upon an area, here referred to as the opening valve part area, arranged on a movable valve part, so that a feedback opening force is generated. The level of the pressure is determined by a closing actuating force acting counter to the opening force. The closing actuating force is created by the force from an electric, hydraulic or pneumatic actuator, such as a solenoid, and/or by the force from a pilot pressure acting upon a pilot area and/or by the force from a biased spring assembly.
The problem with achieving an initially high spring constant which balances the actuating force on a movable valve part is especially marked in the construction of adjustable valves for a shock absorber for a vehicle suspension. In the construction of an adjustable shock absorber valve for a vehicle, there are two conflicting construction requirements. The damping of the unsprung mass, for example the wheels, is best realized with a valve in which the pressure derivative of the flow (dP/dQ) can be varied. The damping of the sprung mass is best realized with a valve in which a pressure level can be set which is independent of the flow. In the prior art relating to pressure level regulation, the pressure level is set by a master control unit, which works out the desired pressure level and sets this by varying the flow to the valve, i.e. by varying the actuating force created, for example, by a solenoid.
A known design within the field of the invention is described by the Applicant's published patent application WO2006135319, in which the closing actuating force of a pilot stage in a shock absorber valve is determined by the force from an actuator.
In this patent application there is described a shock absorber valve/pressure regulator in the form of a pilot-controlled two-stage valve, intended to control a damping medium flow between the two damping chambers of a hydraulic shock absorber. The shock absorber valve comprises a valve housing with at least one main valve having a movable valve part in the form of a main cone disposed between a main valve spring arrangement and a seat, and a pilot valve comprising a pilot slide. The main cone delimits a pilot chamber in the valve housing, in which the valve main spring and the pilot slide are disposed. The characteristics of the shock absorber valve are principally controlled by the pressure build-up in the pilot chamber, which is adjusted by the position of the pilot slide in the pilot chamber. The position is determined by the force balance between the spring force of a pilot spring and the counterholding actuating force from an electrically controlled actuator, but also by the feedback pressure opening force created by the pressure in the pilot chamber. This type of pressure regulator is thus controlled with pressure regulation.
Another variant of a shock absorber valve with regulation of the pilot stage is described in U.S. Pat. No. 5,398,787. Here too, a pressure-regulated pilot stage is shown, in which the position of the pilot cone is controlled by the solenoid force, the spring force and the hydraulic forces against which it works. By virtue of the configuration of the outer dimensions of the pilot valve, the hydraulic forces deriving from a given spring constant are controlled within the whole of the working range. This construction is described as a function of the choice of components and will regulate either as a pressure regulator or as a bleeder valve. Nor in this solution is the possibility indicated of achieving both a bleeder-like character and a pressure regulator character in one and the same valve.
In U.S. Pat. Nos. 5,937,975 and 6,044,939, a further variant of a shock absorber valve is shown. Two springs, a stiff spring and a pliable spring, work in series to regulate the position of the pilot stage. These springs are coupled to enable a certain damping even when the valve is currentless and is ceasing to regulate. The stiff spring is active throughout the normal working range and the pliable spring is only active when the pilot stage is so far open that no further regulation of the damping is possible by varying the pressure balance of the pilot stage. This construction will regulate solely as a bleeder valve. Nor in this solution is the possibility indicated of achieving both a bleeder-like character and a pressure regulator character in one and the same valve.
The pilot valve in patent WO2006135319 can be said to have solely a pressure regulator character, and thus to be only pressure-regulating. The pilot valve in U.S. Pat. No. 5,937,975 can be said either to have a bleeder character, and thus to be purely position-regulated, or to have a purely pressure-regulating character. In a position-controlled pilot stage, a construction is sought in which the position of the pilot cone is fully controlled by the actuating force and the force from the spring against which it works, i.e. it is unaffected by the pressure. The position of the cone shall thus not be affected by either the flow through the valve or the pressure loss across the valve. In the position-regulated pilot stage, which is described in U.S. Pat. Nos. 5,937,975 and 6,044,939, a construction of the pilot valve is sought in which the pressure loss always approaches zero whenever the flow through the valve approaches zero. Essentially, a position regulation produces a valve character in which the opening pressure always starts at zero and increases with increasing flow, whereas a pressure regulation generally produces characters which start at a flow-dependent opening pressure and have a gently increasing pressure as the flow increases.
No solution is known in which pressure regulators having the above characteristics in the form of pressure and position regulation are mutually combined.